Bitumen is a complex mixture of hydrocarbons and hydrocarbon derivatives, including aliphatic, naphthenic and aromatic compounds. The components in bitumen are conventionally classified using four broad component groups: asphaltenes, resins, aromatics and saturates. Asphaltenes are black or brown amorphous solids and are generally considered as highly polar and complex aromatic materials of fairly high molecular weight. Resins are dark brown in colour, solid or semi-solid and very polar in nature. Aromatics are dark brown viscous liquids and typically consist of non-polar carbon chains in which unsaturated ring systems dominate. Saturates are non-polar viscous oils which are straw or white in colour and comprise aliphatic hydrocarbons together with alkyl-naphthenes and some alkyl-aromatics.
Characterisation of the compounds in a bituminous material is typically carried out by extracting the required fraction with a solvent, separating the required compounds from this fraction (using e.g. liquid chromatography) and analysing the separated compounds (using e.g. gas chromatography). Techniques of this type can be used to analyse the saturates, aromatics and resins in a bitumen (the asphaltenes cannot generally be extracted with a solvent and are precipitated using a short alkane such as heptane), but the techniques are complex and time-consuming. Also consecutive solvent extractions and evaporations lead to loss of more volatile compounds in the bituminous material, decreasing the efficacy of the characterisation. The present inventors have sought to provide a simple and effective method of analysing the components that are present in bituminous materials.
Bituminous materials may contain trace amounts of polycyclic aromatic compounds (PACs). During handling of bituminous materials at elevated temperatures (e.g. during road paving or roofing) fumes are emitted that may contain traces of PACs. Although PAC concentrations are small, worker exposure to bitumen fumes is of potential concern because some PACs are considered to be carcinogenic. Brandt et al, in Polycyclic Aromatic Compounds 16 (1999) 21, describe a method of measuring the quantity of PACs in bituminous materials. A sample is subjected to solvent extraction using dimethylsulfoxide in a Flow Injection Analysis coil. The extraction is followed by normal phase liquid chromatography and then gas chromatography. This method is effective but complex. The present inventors have sought to provide a simpler method of analysing bituminous materials that permits the determination of the quantity of PACs.